Field of the Invention
The present invention relates generally to turbocharger systems for applying high pressure air to an internal conbustion engine, and more particularly, to an improved turbocharger system having means for selectively enabling an operator of the vehicle including a turbocharger system to selectively reduce manifold pressure during cruise or other times to improve engine economy.
Modern turbochargers typically comprise a turbine and compressor mounted to a common shaft. The turbine housing includes a gas inlet and gas outlet and is coupled to the exhaust gas manifold of a combustion engine for circulation of the exhaust gases through the turbine housing to rotatably drive the turbine wheel. In turn, the turbine wheel rotatably drives the compressor wheel which compresses ambient air and supplies compressively charged air to the intake manifold of the engine.
It is advantageous to use turbochargers in that substantially higher density fuel-air mixtures can be delivered to the combustion chambers or cylinders of an engine and thereby increase engine performance and efficiency. However with many internal combustion engines, it is desirable to limit the maximum pressure or boost pressure at which charged air may be delivered to the engine at full load engine operating conditions. That is, many turbochargers are capable of delivering charged air to the engine at boost pressures substantially greater than the engine or the turbo charger can withstand. Accordingly, a wide variety of valves and other pressure control devices have been proposed to limit the maximum boost pressure of charged air supplied by the turbocharger compressor. Such boost controls typically open a by-pass flow path around the turbine wheel to by-pass off a portion of the engine exhaust gases out of driving communication with the turbine. Such arrangement utilizes a so called waste-gate valve to limit the maximum allowable rotational speed of the turbine wheel in order to limit correspondingly the maximum allowable rotational speed of the compressor wheel and thereby limit the maximum boost pressure of the charged air supplied to the engine. Structurally, these waste-gate valve arrangements include a control actuator responsive to engine or turbine charger parameters to control the opening and closing of the waste-gate valves and are available in a variety of specific constructions which can be made responsive to any of a selected number or combination of parameters such as compressor inlet pressure, compressor discharge pressure, turbine inlet pressure, or the like.
In some designs, a spring biases the valve to a closed position preventing by-pass of exhaust gases around the turbine wheel until compressor discharge pressure reaches a predetermined maximum. Other designs utilize a spring to bias the valve to an open position and couple the valve to a diaphragm responsive to parameter-indicative pressures to maintain the valve closed against the spring bias until compressor discharge pressure reaches a predetermined magnitude.
In diaphragm control pressure responsive waste-gate valve arrangements of the prior art, the waste-gate valve is maintained in a closed position preventing by-pass of exhaust gases around the turbine wheel whenever compressor discharge pressure is at or below the predetermined maximum allowable magnitude. This is desirable during substantial full load, transient operation, such as acceleration, so that the turbocharger develops substantial boost pressure. However, during part load, steady state cruise operation of the engine, substantial turbocharger boost pressure is not required and it is therefore desirable to open the turbocharger waste-gate valve to unload the turbocharger from the engine. That is, it is desirable during this part-load condition to by-pass exhaust gases around the turbine wheel to reduce back pressure on the engine and thereby correspondingly improve engine efficiency and economy. In the prior art, control actuators for controlling the position of a waste-gate valve have not been designed for the dual purpose of preventing turbocharger overboost as well as for allowing the selective opening of the waste-gate valve during part load, cruise operation. However, recent improvement along this line is disclosed in U.S. Pat. No. 4,377,070 to Alan B. Shadbourne. But the Shadbourne approach continues to accomplish its objective by by-passing the exhaust gas turbine. This has the disadvantage that it continues to achieve its objective by dealing with the extremely hot exhaust gases and therefore requires the use of materials which can withstand such high temperatures and pressures. In accordance with the present invention, it is desired to provide a means for accomplishing the intended objective by dumping the compressed air on the output side of the turbocharger so as to eliminate such disadvantages.